Avoid uncoordinated data processing by both the new and old servers, where multiple
servers could connect concurrently and process the same data. For example, when using
incoming email
, if both GitLab instances are
processing email at the same time, then both instances miss some data.
This type of problem can occur with other services as well, such as a
non-packaged database
,
a non-packaged Redis instance, or non-packaged Sidekiq.